1. Field of the Invention
The present invention is related to a method of manufacturing a semiconductor device, and more specifically, to a method of splitting a wafer, on which semiconductor devices have been formed, into individual chips.
2. Description of the Related Art
During a process of manufacturing a semiconductor device, a wafer on which all elements have been formed is split along dicing lines or chip splitting lines and thus divided into a plurality of chips (also referred to as xe2x80x9cdiesxe2x80x9d or xe2x80x9cpelletsxe2x80x9d). These chips are stuck to an adhesive sheet, and sequentially picked up therefrom. Further steps to complete the manufacturing of the semiconductor devices may include a step of mounting each chip on a lead frame and a TAB tape or a step of sealing the chip into a package.
In recent years, there has been a demand for reduction in the thickness of chips which allows for thinner packages. One way to reduce the thickness of chips is to grind or etch the back surface of a wafer. However, thinner wafers are likely to break during conveyance between various manufacturing steps (manufacturing apparatuses), and cracking or chipping is likely to occur during dicing.
As a method of solving this problem, a manufacturing method called xe2x80x9cdicing-before-grindingxe2x80x9d has been proposed. FIGS. 1A and 1B to FIGS. 7A to 7B sequentially show steps of dividing a wafer, on which all elements have been formed, into individual chips using the method of dicing-before-grinding. FIGS. 1A to 7A are perspective views, and FIGS. 1B to 7B are sectional views.
With the dicing-before-grinding method, various semiconductor elements 22 are first formed in a main surface region of a wafer 21. Then, an element-formed surface 21A of the wafer is diced along dicing lines or chip splitting lines using a diamond blade 23 or the like to form grooves 24A and 24B of a depth slightly greater than the desired thickness (achieved upon completion) of chips (see FIGS. 1A and 1B to FIGS. 4A and 4B). Subsequently, a surface protection film 25 is stuck to the element-formed surface 21A of the wafer 21 (FIGS. 5A and 5B). A wheel 26 with a grindstone is rotated to grind a back surface 21B of the wafer 21 to split the wafer into individual chips 27 while thinning the wafer 21 (FIGS. 6A and 6B). Then, the ground back surface 21B of the chip 27 is mirror-finished by polishing or the like as required to remove streaks resulting from the back surface grinding (FIGS. 7A and 7B).
However, the dicing-before-grinding method serves to remove the streaks on the back surfaces of the chips 27, but fails to remove streaks that may be created on the sides of the chips 27 during dicing or chipping. Thus, the bending strength (or breaking strength) of the chips unavoidably decreases as a result of stress concentration. This in turn leads to cracking of the chips during pick-up or resin-sealing.
As a technique of avoiding this problem, a method has been proposed which comprises wet etching after the back surface of the wafer has been ground. However, this method serves to remove the streaks on the sides of chips but not the chipping on the element-formed surface. Further, a method has been proposed which comprises RIE (Reactive Ion Etching) instead of dicing to form grooves. However, the depth of the grooves that can be formed by RIE is only about 100 xcexcm. This limits the thickness of chips to which this method is applicable.
As described above, the conventional semiconductor manufacturing method using the dicing-before-grinding method leaves much room for improvement because it fails to sufficiently remove streaks that may be created on the sides of chips or chipping that may be formed on the element-formed surface.
Further, several improvements have been proposed but are limited in certain points. Consequently, they are not sufficient to form intended thin chips.
According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device, the method comprising forming notches in an element-formed surface of a wafer on which semiconductor elements have been formed; sticking a surface protection tape to the element-formed surface of the wafer; cleaving the wafer along a crystal orientation using the notches as starting points; and grinding a back surface of the wafer.